Process for the production of



United? rates 3,000,879 PROCESS FOR THE PRODUCTION OFEPSILON-CAPROLACTAMS Benjamin Phillips, Charleston, Samuel W. Tinsley,South Charleston, and Paul S. Starcher, Charleston,W. Va., assignors toUnion Carbide Corporation, a corporation of New York No Drawing. FiledJune 8, 1959, Ser. No. 818,540 6 Claims. (Cl. 260239.3)

This invention relates to the preparation of lactams and moreparticularly to the preparation of epsilon-caprolactams. Moreparticularly, this invention is directed to a non-catalytic process forthe production of epsilon-caprolactams by the heating of thecorresponding 6-hydroxycaproamides in the presence of water at hightemperatures and superatmospheric pressures. This invention is furtherdirected to a non-catalytic process for the production ofepsilon-caprolactams whereby the reaction reaches an equilbrium so thatapproximately 50 percent of the 6- hydroxycaproamides form monomericepsilon-caprolactams while the other 50 percent remains capable ofsubsequent conversion to additional epsilon-caprolactams. Recycling ofthe reactants under the conditions identical to those of the initialreactions produces additional monomeric epsilon-caprolactams. Continuingthe recycling process, yield efficiencies from about 85 to 95 percent of6-hydroxycaproamides to the corresponding epsilon-caprolactams areobtained.

It is an object of this invention to provide a one-step process for theproduction of epsilon-caprolactams. A further object of this inventionis to provide a process for the production of epsilon-caprolactams tothe substantial exclusion of polymerized material and in high yieldefiiciencies of 6-hydroxycaproamides to epsilon-caprolactams. Anotherobject of this invention is to provide a one-step process for theproduction of alkyl-substituted epsiloncaprolactams andN-alkyl-epsilon-caprolactams. These and other objects will becomereadily apparent to those skilled in the art in light of the teachingsherein set forth.

Lactams are used for the production of polyamides suitable for themanufacture of fabrics, films, fibers, coating compositions and thelike. Heretofore, the usual preparation of lactams has been by Beckmannrearrangement of ketoximes. Caprolactam, the most important member ofthis class, has long been prepared by rearrangement of cyclohexanoneoxime. For example, the preparation of the oxime by treatingnitrocyclohexane or its salt with hydroxylamine, hydrogen, sulfur,sodium nitrite and the like is well known in the art. It is also knownto prepare cyclohexanone oxime by treatment of cyclohexanone-bi sulfitecomplexes with nitrous acid and the like processes. More recent priorart discloses methods whereby caprolactams are prepared by reacting anester of epsilon-hydroxycaproic acid alone or with a mixture of anammonium salt of epsilon-hydroxycaproic acid in the presence of anexcess of concentrated aqueous ammonia solution under conditions ofsuperatmospheric pressures and temperature ranges from about 250 C. toabout 300 C.

The present invention is based on the discovery thatepsilon-caprolactams can be produced by heating a reaction mixtureconsisting of a 6-hydroxycaproamide and water, under superatmosphericpressures and at temperatures in the range from about 300 C to about 475C.

The process of this invention is readily accomplished by heating areaction mixture consisting of a 6-hydroxycaproamide and water in thetemperature range of about 300 C. to about 475 C. preferably in therange of about 350 C. to about 425 C. under superatmospheric pressures.The reaction mixture, upon cooling, is subjected to conventionalrecovery procedures such as extraction with Patented Sept. 19, 1-961 icetifiiiti rasur R R R R R wherein R represents members selected from thegroup consisting of hydrogen atoms and alkyl groups.

A preferred class of 6-hydroxycaproamides suitable for use as startingmaterials are those hydroxycaproarnides corresponding to the generalformula set forth above wherein R represents hydrogen atoms and alkylgroups and wherein the total number of carbon atoms contained in saidalkyl groups does not exceed twelve. The preferred starting materialsand resulting products of this process are listed as follows:

Starting Materials Resulting Products fi-hydroxycaproamide2-methyl-6-hydroxycaproamide 3-methyl-6-hydroxyeaproamide 4-methyl-G-hydroxyeaproamide 5-methyl6-hydroxycaproamide6-methyLG-hydroxycaproamide 2-ethyl-6-hydroxycaproamide3ethyl-6-hydroxycaproamide 4-ethyl-G-hydrorwcaproamide 5-ethyl-6-hydroxycaproamide 6-ethyl-6-hydroxycaproamide2,3-dimethyl-G-hydroxycaproamide.

ami e 2 ethy1,3 -methyl-6-hydroxycaproamide.

2 ethyl,4-methyl-G-hydroxyeapro amide 2-ethyl,5 methylG-hydroxycaproamide.

2 ethyl,6- methyl-fi-hydroxycapro amide 3 ethyl,2-methyl-G-hydroxyeaproamide.

3 ethyl,4-methyl-6-hydroxycaproamide.

3 ethyl,5 -methyl-6-hydroxycaproamide. 3 ethyl,6-methy1-6-hydroxyeaproamide.

epsilon,caprolactam. alpha-methyl-epsilon-caprolactambeta-methyl-epsilon-caprolactam. gamma-methyl-epsllon-eaprolaetam.delta-methyl-epsilon ,eaprolactam. epsilon-methyl-epsilon-caprolaetamalphaethyl-epsilon-caprolactam. beta-ethyl-epsilon-caprolactam.gamma-ethyl-epsilon-eaprolactam. deltaethyl-epsilon-caprolactam.epsilon-ethyl-epsilon-caprolaetam.a1pha,beta-dimethyl-epsilon-eaprolactarnalpha,gamma-dimethyl-epsilon-caprolactam.

alpha, delta-dimethyl-epsilon-eaprolactam.

alpha,epsi1on-dimethyl-'e psiloneaprolactam.

beta,gamma-dimethyl-epsilon-caprolactam.

beta, delta-dimethyl-epsilon-caprolactam.

beta,epsilon-dimethyl-epsilon-caprolactam.

gamma,deltadimethyl-epsilon-caprolactam.

gamma epsilon -dimethy1-epsilon eaprolactam.

delta,epsilon-dimethylepsi1on-eaprolactam.

beta beta deltatrimethyl-epsiloncaprolactaru.

beta,delta,delta-trimethyl-epsiloncaprolactam.

alpha,beta,gamma-trimethyl-epsllon-caprolaetam.

alpha ,beta ,epsilon-trirne thyl-epsilon-caprolactam.

alpha,gamma,delta-trimethyl epsilon-caprolactam.

alpha, gamma,epsilon-trimethylepsilon-eaprolactam.

gamma,delta,epsilon-trimethyl-epsilon-caprolactam.

alpha -ethyl beta-methyl-epsiloneaprolactam.

alpha ethyl gamma methyl epsilon-eaprolactam.

alpha ethyl delta-methyl-epsiloneaprolactam.

alpha-ethyl epsilon methyl epsilou-caprolactam.

beta ethyl alpha -methy1-epsilo'n- 'caprolaetam.

beta ethyl gamma methyl epsi- 'lon-caprolactam.

beta ethyl delta methyl-epsiloncaprolactam.

beta ethyl-epsilon-methyl-epsiloneaprolactam.

Starting Materials Resulting Products 4 ethgLZ -methy1-6-hydroxycapro- 6ethyl,2 -methyl-6-hydroxycaproamide.

6 ethyl,3 -methyl-6-hydroxyeaproamide am2,2-dimethyl-6-hydroxyoaproamide 3,3-dimethyl-G-hydroxycaproamide.4,4dimethyl-fi-hydroxycaproamide.

2,2,3 trimethyl 6 hydroxycaproannde.

3,3,4 trimethyl 6 hydroxycaproamide.

4,4,6 trimethyl 6 hydroxycaproamide.

5,5,2 trimethyl 6 hydroxycaproamide 3,3 dimethyl 4 ethylfi-hydroxyoaproamide.

4,4 dimethyl 2 ethyl G-hydroxyoaproamide.

N-methyl-S-hydroxyeaproamide N -ethyl-6-hyd ro Xycaproamide N-propyl-6-hydroxycaproamid N-butyl-fi-hydroxyeaproamide N-pentyl-6-hydroxyeaproamid N-hexyl-G-hydroxycaproamideN-methyl-fi-hydroxycaproamide N butyl -2 methyl 6 hydroxycaproamrde.

N methyl 3 methyl 6 hydroxycaproamide.

N ethyl 4 methyl 6 hydroxycaproamide.

N propyl 5 methyl 6 hydroxycaproamrde.

N pentyl; 6 methyl 6 hydroxycaproarnrde.

N methyl 3 ethyl 6 hydroxycaproamide.

N butyl 2,3-dimethyl-6-hydroxycaproarrude.

N -me thyl-2,5-dimethyl-G-hydroxycaproarnide.

N propyl-3,4-dimethyl-G-hydroxycaproarnide.

N butyl 4,5-dimethyl-6-hydroxycaproarnidev N methyl 3,3,5-trimethyl-6hydroxyeaproanude.

N ethyl 2,4,6 trimethyl 6 hydroxycaproamide.

N propyl 4,5,6 trimethyl-Ghy droxyoaproamide.

N-butyl 2 ethyl 4 methyl-G-hyhydroxycaproamide.

N methyl 3 ethyl 5 methyl-6 hydroxyoaproamide.

N propyl 4 ethyl 6 methyl-6- hydroxycaproamide.

N methyl 6 ethyl 4 methyl-6- N hydroxyoaproamide.

N-propyl-4,4 -dimethyl-6-hydroxyeaproamide.

N methyl 4,4-dimethyl 2-ethyl- (i-hydroxycaproamide.

gamma ethyl alpha methyl -epsilon-caprolactam.

gamma ethyl beta methyl epsilon-caprolactam.

gamma ethyl delta methyl epsilon-caprolactam.

gamma ethyl epsilon methylepsilon-caprolaetam.

epsilon ethyl alpha methylepsilon-caprolactam.

epsilon ethyl beta methyl epsilon-caprolactam.

eps lon ethyl gamma me thylepsilon-caprolaotam.

epsilon ethyl delta methyl epsilon caprolactam.

alpha, alpha dimethyl epsilon oaprolactam.

beta, beta dimethyl-epsilon-caprolactarn.

gamma, gamma dimethyl-epsiloncaprolactam.

alpha, alpha, beta trimethyl epsilon-eaprolactam.

beta, beta, gamma trimethyl epsilon-caprolactam.

gamma, gamma,epsilon trimethylepsilnn-caprolactam.

delta, delta, alpha trimethyl epsilon-caprolactam.

beta, beta -dimethyl-gamma-ethylepsilon-caprolaetam.

gamma, gamma dimethyl alphaethyl-epsilon-caprolactam.

N-rne thylepsilomcaprolactam.

N ethyl-epsilon-caprolactam.

N-propyl-epsilon-caprolactam.

N-hutyl-epsilon-caprolaetam.

N -pentyl-epsilon-caprolactam.

N-hexyl-epsilon-caprolactam.

N-methyl-epsilon-caprolactam.

N-llexyl-epsilon-caprolaotam.

Nbutyl alpha methyl epsilon caprolactam.

N methyl beta methyl epsilonceprolactam.

N ethyl gamma methyl-epsiloncaprolactam.

N propyl delta methyl epsiloneaprolaetam.

N-pentyl epsil0n-methyl-epsiloncaprolactam.

N methyl beta ethyl epsilon caprolactam.

N butyl alpha, beta dimethyl epsilon-caprolaetam.

N methyl alpha, delta-dimethylepsilon-eaprolactam.

V N propyl-beta,gamma-dimethy1- epsilon-caprolaotarn. Nbutylgamma,delta-dimethyl epsilon-caprolactam. N methyl beta, beta,delta tri methyl-epsilon-oaprolactam1 N-ethyl-alpha, gamma,epsilon-trimethyl-epsilon-caprolaetam. N propyl gamma, delta, epsilontrimethyl-epsilon-caprolactam. N butyl alpha ethylgammamethyl-epsil0n-caprolactam.

N methyl beta ethyl delta methyl-epsilonpaprolactam.

N propyl gamma ethyl epsilonmethyl-epsilon-eaprolactam.

- methyl epsilon -ethyl-gamma;-

methylepsilon-oaprolactam.

N propyl gamma, gamma di methyl-epsilon-caprolactam.

N methyl gamma, gamma di methyl alpha ethyl epsiloncaprolaotam.

The time of reaction is not necessarily critical and may vary from 10minutes to as much as a day depending on the reaction conditions. Mostdesirably, conditions are adjusted so as to complete the reaction inabout one to three hours.

The term superatmospheric pressure as used herein is defined as thepressure produced by the reactants on heating in a closed vessel orhigher pressures if desired. This pressure is maintained for theduration of the reaction. The term lower alkyl as used herein isintended to mean saturated, unsubstituted hydrocarbon chains containingfrom one through eight carbon atoms per chain. Typical lower alkylgroups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,tertiary-butyl, amyl, hexyl, heptyl, octyl and the like.

The following examples served to illustrate the invention.

Example I A solution of 300 grams of 6-hydroxycaproamide (melting point54 C.) in 900 grams of water (25 percent solution) was heated for threehours in a stainless steel bomb (three-liter) at 350 C. and autogenouspressures. The reaction mixtures from two such duplicate runs werecombined and extracted four times with 700- milliliter portions ofchloroform. The chloroform extracts were distilled and there wasrecovered 157 grams epsilon-caprolactam characterized by the followingphysical properties: boiling point, 112 C. at 2.5 millimeters; meltingpoint, 67 C. The yield was 30.4 percent of the theoretical.

In an analogous manner as the above example N-methyl-epsilon-caprolactamis prepared from N-methyl-6-hydroxycaproamidc.

Example II A run made exactly as Example I except that the solutionheated was a 10 percent solution of 6-hydroxycaproamide in Water gave a31 percent yield of epsilon-caprolactam (melting point, 67-68 C.).

Example III A solution of 300 grams of 3-methyl-6-hydroxycaproamide in900 grams of water (25 percent solution) is heated for three hours in astainless steel bomb (threeliter) at 350 C. and autogenous pressures.The reaction mixtures from two such duplicate runs are combined andextracted four times with 700-milliliter portions of chlorofrom. Thechloroform extracts are distilled to yield 184 grams ofbeta-methyl-epsilon-caprolactarn. The yield is 35.0 percent of thetheoretical.

Example IV ROE Ill

wherein R represents members selected from the group consisting ofhydrogen and lower alkyl groups, in water at temperatures ranging fromabout 300 C. to about 475 C. at superatrnospheric pressures.

2. The process of claim 1 in which the temperatures range from about 350C. to about 425 C.

3. The process of claim 1 wherein the hydroxycaproamide used is6-hydroxycaproamide to produce epsilon caprolactam.

4. The process of claim 1 wherein the hydroxycaproamide used is3-methyl-6-hydroxycaproamide to produce beta-methyl-epsilon-caprolactam.

5. The process of claim 1 wherein the hydroxycaproamide used is3,S-dimethyl-6 hydroxycaproamide to producebeta,delta-dimethyl-epsilon-caprolactam.

6. The process of claim 1 wherein the hydroxycaproamide used isN-methyl-6-hydroxycaproamide to produce N-methyl-epsilon-caprolactam.

No references cited.

1. A PROCESS FOR THE PRODUCTION OF AN EPSILON-CAPROLACTAM WHICHCOMPRISES HEATING A 6-HYDROXYCAPROAMIDE, CHARACTERIZED BY THE STRUCTURALFORMULA: